Method of coating abrasive particles



NOV. 3, 1936. I N r A 2,059,983

METHOD OF COATING ABRA SIVE PARTICLES Filed June 27, 1932' INVENTORS Patented Nov. 3, 1 936 UNITED STATES PATENT OFFICE I METHOD or COATING ABRASIVE PARTICLES Application June 27, 1932, Serial No. 619,599

6 Claims. (01. 51-278) The present invention relates to a method of coating particles with substances having a lower melting point than the particle, and more particularly to a method ofcoating particles of an abrasive material with a coating and bonding material whereby the coated particles may be readily pressed together in any desired shape of grinding or abrading wheel.

The invention provides a method of uniformly coating particles whereby the particles may be obtained as dry, separate individuals which, at the temperature of collection, do not cohere one to the other.

The invention further provides a method of coating abrasive particles with bonding and coat- .ing material whereby the coated particles may subsequently be pressed together atv the proper temperature thus causing the particles to cohere.

The invention also provides a method for producing grinding wheels in which the particles of abrasive are coated substantially uniformly and in which there are substantially no voids between adjacent particles.

The invention further provides a method of making a grinding wheel in which the particles of abrasive are held together by organic material of'resinous type rather than by a fused ceramic material.

In the drawing:

. Fig. 1 is a showing of a form of apparatus in which certain steps of the herein described process may be performed.

Fig. 2 is an enlarged section of one of the coated particles. I

Fig. 3 is an enlarged view substantially in line III-III of Fig. 1.

The drawing depicts a form of apparatus in which the process of the present invention may be performed. It will be understood, however,

that any convenient form of means or apparatus may be used in performing these various steps. A

coating tower or chamber is indicated generally at H), and in the form shown, comprises an upright chamber or tower in which a moving stream of air may be confined and which is provided with suitable means for the entrance and exit of the air stream and of particles which may be carried by the air stream. The chamber or tower I0 is provided adjacent its lower end with an inlet port H which is in fluid communication with any conventional type of means for insuring a flow of gaseous fluid, as for instance the blower l2. Powdered coating material is fed into the air stream from a convenient and suitable source as for instance by discharging the powdered coating material from a container l3. The finely powdered coating material is suspended in an air stream by the force and turbulence of compressed air or gas discharged into the container through the valved conduit [4 and thereafter is carried'into the tower 5 through the inlet I l and is thereafter moved upwardly through the tower with the air stream induced by the action of blower l2.

A heated particle container 15 is placed adjacent the top of the coating tower It) in which 10 particles of abrasive or other material to be coated are placed and heated to the desired temperatures. This heating operation may be done by any suitable form of heating device whereby the temperature of the particles It in the con- 15 tainer may be heated to and maintained at a temperature above the melting point of the coating material, but somewhat below the melting point of the material of the particles to be coated. When coating particles of abrasive with certain 20 organic materials these temperatures are above 40 C. and below about 800 C. or a temperature at which chemical change or fusing does I not occur in the abrasive. That is, the particles to. be coated, for instancaparticles of abrasive 25 material suitable for use in the preparation of grinding wheels and the like, are heated to the desired temperature in the particle container l5 and are admitted to the coating tower at a point adjacent the top thereof through a suitable pas-, 0 sage means, as for instance through the chute l1 leading from the particle heater Hi to the top of the coating tower and distributed over the spider l8.

The coating tower I0 is also provided with an 35 off-take l9 adjacent the top thereof through which the current of gaseous material moving from the bottom of the tower to the top thereof. may be led away and discharged. Means may also be provided for collecting and re-claiming-any ex-, 40 cess coating material passing outwardly through the top of the coating tower.

After the abrasive particles have been .admitted to the top of the tower l0, due. to their larger particle size and to their greater specific grav- 45 ity, they fall downwardlyto the bottom of the tower through the upwardly moving current of gaseous material which may be air or in some cases a neutral gaseous atmosphere, and during such movement from the top of thatower to the 50 bottom thereof, come in contact with the upwardly moving powdered coatingmaterial 20.

The particles of heated abrasive in falling downwardly through the tower come in contact with the powdered coating material and, since 55 the particles of abrasive have been heated to a sufliciently high degree and are at a temperature above the melting point of the coating material, transmit heat to the particles of powdered coating material causing them to melt and enclose and envelope the abrasive particles. By regulating the temperature to which the abrasive particles have been heated and therefore the quantity of available heat in the particles, the heat required to melt the powdered coating material and the heat carried away from the abrasive particles by the upwardly moving current of gas, lower the temperature of the coated particles sufliciently to allow the fused and enveloping coating material to harden and solidify so that these particles upon collection at the bottom of the coating tower are substantially separate and individual particles which do not adhere to the rest of the particles in the mass.

The coating material is usually of a type which does not react chemically with the abrasive particles or react chemically with the upwardly moving current of air at the temperatures obtaining within the coating tower. The type of coating material which we have found preferable for this use comprise solid resins and resin like materials, either of natural or synthetic origin and include those materials of a melting point above 40 C. as for instance, resin like substances obtained by condensation oi phenols and aldehydes.

We prefer to use resinous materials of the type generallyknown as thermo setting resin so that the coated particles of abrasives may be subsequently formed in the desired shape, as for instance, in the form of a grinding wheel, by use of heating and pressing operations which are known in the art. When the coated particles are used for this purpose it is necessary to control the amount of coating uponthe abrasive particle by regulating the size of the powdered coating material, the velocity of the upwardly moving stream and the temperature of the coated particles. By such control the abrasive particles carry a coating, the volume of which may be as much as 30% of the total volume of the coated particles. Where the coated particles are to be used for abrading or grinding wheels, we have found that grinding wheels of excellent quality can be obtained where the volume of coating is about 15% of the total volume of the coated particles and in some cases less than this amount. This is shown clearly in Fig. 2 where the abrasive particle is shown at 2| surrounded by an exterior coating of resinous material 22 which completely encloses the abrasive particle and which when heated and pressed with similar coated abrasive particles may be formed into the desired shape or form as the binding material fuses-and coalesces to hold the particles together.

As an example pounds of grit or abrasive, heated to about 150 C. produce, pounds of coated particles when falling through a stream of resin of the type known to the trade as Durez and collected on the belt 25 as individual particles suitable for use in the preparation of a grinding wheel.

What is claimed is: i

1. The method of coating abrasive particles with a thermo-setting resinous material of lower melting point than the particles which comprises moving the powdered resinous material upwardly in a current of a gaseous medium and dropping heated particles of abrasive downwa dly through said current and said material whereby upon application of heat thereto.

2. The method of coating abrasive particles with a thermo-setting resinous material which comprises moving the material upwardly in a current of a gaseous medium, and dropping particles of the abrasive heated to a temperature above the melting point of the coating material downwardly through said current and said material whereby the heated particles come into contact with the resinous material melting the material and being enclosed thereby, the resinous material coating the particles being capable of hardening upon application of heat thereto.

3. The method of coating abrasive particles with a thermo-setting resinous material the fusion point of which is above 40 C. which comprises moving the material upwardly in a current of a gaseous medium, and dropping particles of the abrasive heated to a temperature above the melting point of the coating material and below the fusion point of the abrasive downwardly through saidcurrent and said material whereby the heated particles come into contact with the resinous material melting the same and being enclosed thereby and cooled and solidified by the current of gas, the resinous material coating the particles being capable oi hardening upon application of heat thereto.

' 4. The method of coating abrasive particles for subsequent use in preparation of grinding wheels which comprises moving a powdered thermo-setting resinous material upwardly in a current of a gaseous medium and dropping heated particles of abrasive downwardly through said current and said material whereby the heated particles come into contact with said resinous material melting the same and being enclosed by the material and cooled and solidified by the current of gas into individual coated particles, capable of being formed into an abrasive article and hardened upon application of heat.

5. The method of making grinding wheels which comprisesv coating abrasive particles with a thermo-setting resinous coating material by moving the powdered resinous material upwardly in a current of a gaseous medium, dropping heated abrasive particles downwardly through said current and said material whereby the heated particles contact with the powdered resinous material melting the same and being enclosed thereby, the current of gas cooling the coated particles to separable individuals, the resin coating still retaining its thermo-setting property and subsequently pressing the coated particles at an elevated temperature to the desired size and shape.

6. The step in the process of making grinding wheels which comprises moving a powdered thermo-setting resinous material upwardly in a current of a gaseous medium, and dropping heated particles of abrasive downwardly through said current and said material whereby the heated particles come into contact with the resinous material melting the same and being enclosed by the material, the coating upon said particles still retaining its thermo-setting property.

HARRY M. DENT. ARTHUR J. NORTON. 

